FIELD OF THE INVENTION
The invention concerns a compression refrigeration unit with a compressor, a gas refrigeration unit, an expansion apparatus, and an evaporator, which are connected to one another in a circulation unit, which contains a coolant.
Such a compression refrigeration unit is, for example, known from WO 90/07683. This known unit is constructed as a transcritical unit--that is, it has a transcritical design. Carbon dioxide is used as a coolant.
A compression refrigeration unit of the initially mentioned type is also known from WO 94/14016. This known unit also works transcritically with carbon dioxide as a coolant.
In order to attain a maximum refrigerating capacity co-efficient with these known transcritical compression refrigeration units, the coolant pressure on the high pressure side is set in a precisely suitable manner within relatively narrow limits. That is attained in accordance with the aforementioned WO 94/14016 by setting the degree of filling of the coolant, which is defined as the quotient of the coolant filling to the total volume in the unit, at a value between 0.55 and 0.70 kg/L in the unit, preferably at 0.60 kg/L. The critical density of carbon dioxide as the coolant is 466 g/L--that is, with this known unit, the degree of filling of the coolant is on the order of 120% to 150%, preferably, on the order of 130% of the critical density. As a result of this degree-of-filling range, there is a maximum of the refrigerating capacity co-efficient with the known transcritical unit in accordance with WO 94/14016. In order to be able to maintain this high degree of filling of the coolant optimally with various average external temperatures at which the unit is used, the proposal is made there that the compression refrigeration unit be constructed with an additional coolant storage unit. The storage unit there is also used to hold excess carbon dioxide when a certain pressure at rest is exceeded on the low pressure side of the unit--for example, with a shutdown in a hot environment. The pressure at rest with a degree of filling f=0.60 k/L is 155 bar at, for example, 60.degree. C.--that is, with a motor vehicle standing in the sun or with a hot engine space.
The goal of the invention is to produce a compression refrigeration unit of the initially mentioned type which is constructed in a comparatively simple manner and which can be used in a relatively large external temperature range without any problems, without substantially impairing the refrigerating capacity co-efficient of the unit thereby.
This goal is attained with a compression refrigeration unit of the initially mentioned type in accordance with the invention by having the degree of filling of the coolant between 50% and 100% of the critical density of the coolant. The pressure at rest of the unit in accordance with the invention is only approximately 105 bar, at, for example, 60.degree. C. and a degree of filling f=0.3 kg/L, corresponding to approximately 2/3 of the degree of filling of known units of the initially mentioned type. This means that, advantageously, as a result of the reduced pressure, fewer compressor shaft seals, for example, are required and thus can be more simply dimensioned. Carbon dioxide is preferably used as a coolant. Carbon dioxide is advantageously equivalent to waste in industrial production and is thus available at a very low cost. Carbon dioxide, in fact, has been known as a coolant already since the transition from the 19th to the 20th century.
With the unit in accordance with the invention, the degree of filling of the carbon dioxide coolant is preferably between 0.25 and 0.45 kg carbon dioxide/L total volume of the cyclic process unit. The degree of filling of the unit is actually constant in accordance with the invention. The degree of filling can be set hereby as a function of the average external temperature of the climatic region in which the unit in accordance with the invention is used. This means that the degree of filling can be selected greater with increasing external or ambient temperature.
Preferably, the compression refrigeration unit in accordance with the invention is constructed transcritically. Of course, the unit in accordance with the invention can also be operated subcritically.
Other details, features, and advantages can be deduced from the following description of the embodiment examples of the compression refrigeration unit in accordance with the invention, indicated schematically in the drawings. It shows: